This invention relates to a system and method for the control of cylinder output torque in an internal combustion engine and more particularly, to a system and method which selectively controls the torque output of each individual cylinder within an internal combustion engine to effect a controlled balancing of the power produced by each cylinder of the engine.
Valve timing systems, arrangements, and assemblies are used in internal combustion engines in order to alter the timing of the opening and closing of the engine""s intake and/or exhaust valves. Prior valve timing systems, typically include one or more camshafts and cam timing assemblies which selectively advance and/or delay the rotation of the one or more camshafts, thereby controlling the actuation of the intake and exhaust valves.
These prior systems and valve timing profiles used by these systems suffer from several drawbacks. Particularly, these prior cam-driven systems rely solely on the physical cam lobe profile ground into the camshaft to raise and lower the individual valves. The general power and/or torque production of an engine is the combined function of all its cylinders. The power production of each individual cylinder is a function of its valve timing as the control for the intake of the fresh fuel/air mix and the subsequent exhaust of the burnt fuel gases. Therefore, the engine""s cylinder-by-cylinder power production relies on the design of the valve timing profile of the camshaft.
In production engines, the camshafts are produced with a fixed cam lobe for each valve of the engine. The camshaft production process makes each intake valve cam profile identical and each exhaust valve cam profile identical for each cylinder. This assumes that each cylinder, piston, and accompanying cylinder head combustion chamber is produced within the given and allowable tolerances, which will result in an engine that produces a substantially similar amount of power and torque from each cylinder.
In practical terms, production and manufacturing tolerances can vary distinctly and cause cylinder to cylinder power imbalances upon the engine""s initial construction. Additionally, as the engine ages, cylinder components can wear at different rates, carbon and combustion byproducts can build up in the combustion chamber in varying degrees, and tolerances may open, all causing new or added engine power imbalance. More importantly, since the lobes of a mechanical camshaft are physically fixed within the engine with no ability to adjust or compensate for the power variances between the individual cylinders, the engine must continue to operate with the power imbalance causing vibration, inefficiency, and possible mechanical damage.
In other words, due to the inability of these prior systems to dynamically adjust the timing of the valves to compensate for different power outputs from each cylinder, the engine will operate in an unbalanced condition throughout its service life. As a result, the engine cannot work to full efficiency and will have vibration, shifting, and drivability problems.
Efforts have been made to increase the efficiency of vehicle engines by eliminating the camshafts and operating the intake and exhaust valves through the use of selectively controllable electromagnetic actuators. These types of systems eliminate many problems related to the physical characteristics of cam-driven systems and offer additional precision in valve timing. However, these prior camless systems are typically implemented for the purpose of improving fuel economy and emissions and do not address the imbalance between cylinders.
There is therefore a need for a new and improved valve timing system for use with a camless engine which overcomes the drawbacks associated with cylinder to cylinder power imbalances. The Applicants"" invention addresses these drawbacks and provides a system and a method for dynamically controlling the valve timing events of the camless engine and which compensates for the effects of cylinder to cylinder power imbalances.
It is a first object of the invention to provide a system for cylinder to cylinder torque control in an internal combustion engine, which overcomes at least some of the previously delineated drawbacks of the prior systems, devices, and/or methods.
It is a second object of the invention to provide a method, strategy, or methodology for actuating an engine""s intake and exhaust valves in a manner which balances the torque or power output of all cylinders of the engine.
According to a first aspect of the present invention, a valve timing system is provided for use with an internal combustion engine including a cylinder having at least one valve. The system includes at least one actuator which selectively actuates the at least one valve; a torque monitoring sensor which is operatively disposed within the cylinder and which is effective to measure a torque output of the cylinder and to generate a signal representing the measured torque output; and a controller which is communicatively coupled to the torque monitoring sensor and to the at least one actuator, the controller being effective to receive the signal and to cause the at least one actuator to actuate the at least one valve according to a predetermined timing profile, the controller being further effective to selectively alter the predetermined timing profile based upon the received signal, thereby selectively altering the torque output of the cylinder.
According to a second aspect of the present invention, a method is provided for controlling the valve actuation of a camless internal combustion engine of the type including a first cylinder and a second cylinder each having at least one valve which is selectively actuated for a certain duration of time. The method comprising the steps of: monitoring the actuation of the valves; monitoring a torque output of the first and second cylinders; comparing the torque output of the first cylinder to the torque output of the second cylinder; and dynamically altering the certain duration of time that the at least one valve within the first cylinder is actuated, effective to cause the torque output of the first cylinder to be substantially equal to the torque output of the second cylinder.
Further objects, features, and advantages of the invention will become apparent from the following detailed description of the preferred embodiment of the invention and by reference to the following drawings.